The present invention relates to an ion implantation apparatus for use in integrated circuit manufacturing, and more particularly to monitoring of a turbo pump in an ion implantation apparatus.
An ion implantation apparatus for use in manufacturing integrated circuits introduces impurities into a silicon or gallium arsenide target by providing impurities to an ion source, extracting the impurities in the form of an ion beam, accelerating the ions to a desired energy, and directing the ion beam to implant the impurities in the target. The concentration of impurities introduced into the target can be precisely determined by measuring the current of the ion beam using a Faraday cup, where the dose is the total number of ions in the current.
For ion implantation, high energy implant processes that can freely control the impurity profile in the interior of silicon substrates are increasingly important. Thus, tandem acceleration principles, such as described in U.S. Pat. No. 3,353,107, which is hereby incorporated by reference in its entirety, are often used to accelerate ions to high energy and implant the ions in silicon substrates. Typical tandem acceleration techniques produce a negative ion beam by combining a positive ion source and a charge exchange cell, or by using a sputter type negative. ion source. The negative ion beam is directed toward an accelerator terminal that is at high positive terminal voltage and accelerated to the terminal voltage.
Then, electrons are stripped from this accelerated negative ion beam in the accelerator terminal by causing the beam to pass through a gas or thin foil that converts the beam into a positive ion beam. This positive ion beam is accelerated to ground potential from the high positive potential of the accelerator terminal and acquires its final energy.
U.S. Pat. No. 4,980,556 and U.S. Pat. No. 5,300,891, which are hereby incorporated by reference in their entirety, disclose examples of apparatuses using the tandem principle. One specific example is a Genus Inc. Model G1500 high energy ion implantation apparatus. FIG. 1 illustrates a known high energy ion implantation apparatus, which is the Model G1500 modified by omitting a pre-acceleration tube now used on the Model G1500. In this apparatus, a hot-cathode PIG (Penning Ion Gauge) ion source 1 produces positive ions. Applying a high positive voltage on ion source 1 extracts these positive ions as a beam. The extracted positive ion beam collides with magnesium vapor when passing through a charge exchange cell 2 which is encountered immediately after ion source 1, and some of the positive ions in the positive ion beam pick up two electrons from the magnesium, so that the positive ion beam becomes a negative ion beam.
After charge exchange cell 2, a pre-analyzing magnet 3 separates ions according to their charge-to-mass ratio so that only the negative ions having a desired energy are injected toward a tandem accelerator 6 which includes a low-energy acceleration tube 7, a stripper canal 8 and a high-energy acceleration tube 10.
A quadrupole magnetic lens 4 furnished at an entrance aperture part of a low-energy acceleration tube 7 of tandem accelerator 6 focuses the mass-analyzed negative ion beam and creates a beam waist. Then, a beam neutralizer (gas cell) 5 neutralizes the focused negative ion beam before entering accelerator 6 where the negative ion beam is accelerated.
When passing through stripper canal 8, the negative ion beam loses orbital electrons by colliding with nitrogen gas that is introduced into stripper canal 8 to convert the beam to a positive ion beam. Since the collision produces a great number of ions charged with various energy levels, accelerator 6 is grounded by a grounding rod 9 as to prevent charging of accelerator 6.
A post-quadrupole lens 11 further focuses the ion beam from high-energy acceleration tube 10, and a post-analyzing magnet 12 separates ions of the beam according to the charge to-mass ratios of the ions and introduces the beam into a process chamber 13 containing a target such as a silicon wafer.
FIG. 2 shows a basic construction of beam neutralizer 5. As shown in FIG. 2, beam neutralizer 5 is a gas cell that is in communication with a gas inlet 16, and a turbo molecular pump 14 which circulates the gas in the cell and creates a high vacuum state in a vacuum region of the ion implantation apparatus. Even if a large amount of gas such as H2, N2, O2, etc. is introduced into the apparatus, differential pumping keeps the gas out of the vacuum region such as process chamber 13 (FIG. 1). Inside beam neutralizer 5, the negative ion beam collides with the gas and is neutralized.
Turbo pump 14 operates on a three-phase alternating current supplied from a power supply 15. However, the apparatus does not have a means for monitoring the operation of turbo pump 14 and cannot immediately detect abnormal operation of turbo pump 14. If turbo pump 14 does not operate properly, the ion beam is not neutralized and accelerated as required, and thus a serious process failure occurs. The abnormal operation can occur due to a malfunction of turbo pump 14, insufficient voltage from power supply 15 to turbo pump 14, or an overload of turbo pump 14.
According to an aspect of the present invention, an ion implantation apparatus for use in manufacturing integrated circuits includes a beam neutralizer for neutralizing an ion beam passing therethrough. The beam neutralizer has a turbo pump that circulates a neutralizing gas inside the beam neutralizer and provides a high vacuum state in a vacuum region of the apparatus. A power supply provides three-phase AC power to the turbo pump, and a current detector measures a current flowing to the turbo pump. A display device or screen displays information about the current. A main controller of the apparatus controls overall operation of the apparatus, and particularly, determines whether the measured current is within a specified range. If the current is not within the range, the main controller generates a power control signal, halts the ion implantation operation, and turns off the turbo pump.
Alternatively, the current detector can measure the current flowing to the turbo pump, determine whether the measured current is within a specified range, and generate the power control signal if the current is not within the range. A display device or screen displays information about the current. In response to the power control signal, the main controller of the apparatus controls can halt an ion implantation operation when the current is out of the desired range.
According to another aspect of the invention, a method for monitoring a turbo pump of an ion implantation apparatus includes measuring a current flowing to the turbo pump, determining whether the measured current is within a specified range, generating a power control signal if the current is not within the range, and stopping the power to the turbo pump in response to the power control signal. The method can further include displaying and storing information about the current respectively on a display and in a memory.